Jean-Baptiste Kammerer

A Hall effect sensors network insensitive to mechanical stress

Hall effect devices are widely used as magnetic sensors in integrated technology. Since they are very sensitive to mechanical stress, they are not suitable for the design of systems subjected to vibrations (portable systems, automotive applications,...). To cancel this cross-sensitivity, the spinning current method may be used. Nevertheless, this method does not remove, but modulates, the mechanical signal. Vibrations whose frequencies are close to the spinning frequency are thus rejected in the base band. Here, we propose an alternative based on a Hall effect sensor network. This method totally removes the mechanical signal and may be combined with the spinning current method in order to reject the flicker noise of the sensor. Compared experimental results obtained with Hall effect sensors subjected to vibrations are presented and discussed.

Design and modelling of a voltage controlled N-well resistor using the MOS tunneling diode structure

In standard CMOS technologies, only N-well or polysilicon resistors are available. The main drawback of these resistors is that their value is not perfectly controlled due to process dispersion. Furthermore, their absolute value is relatively low. Then, when large resistances are needed, the only issue is to implement very long resistors which require large silicon area. In this paper, a new N-well resistor using the MOS tunneling diode structure is presented. This particular structure, which is compatible with any CMOS process, gives the opportunity to increase and to tune the device resistance. As a consequence, this device can be seen as a voltage controlled resistor (VCR). With a CMOS 0.6 /spl mu/m technology, /spl plusmn/10% tuning range and/or up to 20% silicon area saving has been reached. A continuous and smooth compact model for the VCR is also presented. This model can be easily implemented in a high-level analog description language such as VHDL-AMS.

CMOS 3D Hall probe for magnetic field measurement in MRI scanner

This paper presents a 3D Hall probe integrated in a 0.35μm CMOS technology and dedicated to the measurement of the magnetic field gradients in a MRI scanner. It features a 3D Hall device and three instrumentation chains which suppress the MRI main magnetic field and amplify dedicated magnetic field gradients. The unique relationship between the space coordinates in the scanner bore and the magnetic field gradients allows determining accurately the location of the Hall probe inside the bore. First experimental results show that the proposed 3D Hall probe could be used for a MRI tracking system with a sub-millimeter spatial resolution. It is a first step towards the instrumentation of MRI-compatible minimally-invasive surgical tools.

3T MRI scanner magnetic gradient mapping using a 3D Hall probe

The unique relationship between Magnetic Resonance Imaging (MRI) scanner bore space coordinates and magnetic field gradients used in MRI allows building a location system based on the measurement of these gradients. For the first time, these magnetic gradients are accurately measured thanks to a miniature 3D Hall probe integrated in a low cost, low voltage 0.35μm CMOS process. The magnetic gradient 3D map of a 3T MRI scanner has been measured and experimental results show that a sub-millimeter location of the probe is possible. It opens the way for the development of MRI compatible magnetic tracking systems integrable in a surgical tool.

Analysis of the efficiency of spinning-current techniques thru compact modeling

Hall-sensors integrated in CMOS technology are good candidates for the design of low-cost magnetometers. However, one of their major limitations is the 0-field offset, and it is essential to take this effect into account in the very early steps of the design process. For this purpose, we recently developed a new compact model for horizontal cross-shaped Hall-effect device. It is based on physical considerations and takes all the device offset sources into account. For applications where the offset issue is critical, the well known spinning-current technique (SC) can be used to reduce the offset. In this paper, we first analyze the efficiency of four different implementations (number of phases, type of bias) of the SC technique on the different offset sources. Second, we compare these SC techniques by Monte-Carlo analysis. Simulations lead to several interesting conclusions, such as the fact that the best offset cancellation is achieved with the 4-phases SC and a current bias.

Hall-effect magnetic tracking device for Magnetic Resonance Imaging

The unique relationship between the coordinates in the bore of a Magnetic Resonance Imaging (MRI) scanner and the magnetic field gradients used for MRI allows building a localization system based on the measurement of these gradients. We have previously presented a miniature 3D Hall probe integrated in a low cost, low voltage 0.35μm CMOS chip from which we were able to measure the magnetic gradient 3D maps of 1.5T and 3T MRI scanners. In this paper, this 3D Hall probe has been integrated in a magnetic tracking device prototype and an algorithm was built to determine the position of the probe. First experimental results show that the probe gives its position with accuracy close to a few millimeters, and that sub-millimeter localization in a one-shot-3ms-measurement should be readily possible. Such a prototype opens the way for the development of MRI compatible real time magnetic tracking systems which could be integrable in surgical tools for MR-guided minimally-invasive surgery.

Towards a Hall effect magnetic tracking device for MRI

This paper presents the first prototype of a magnetic tracking device for Magnetic Resonance Imaging. The unique relationship between the space coordinates of a MRI scanner bore and the magnetic field gradients used in MRI allows building a localization system based on an accurate measurement of these gradients. These gradients are measured thanks to a 3D Hall device with a footprint of only 50μm2, integrated with its specific conditioning circuit in a low cost, low voltage 0.35μm CMOS process. The first experimental results show that a sub-millimeter localization is possible. It opens the way to the development of MRI compatible magnetic tracking systems integrable in a surgical tool.

Ageing sensor for analog application

We present an analytical CMOS transistor ageing model based on hot-carrier induced degradation. Then we show how such a model can be used to forecast and understand the drift of the main characteristics of a CMOS circuit. Further we demonstrate that this model can be used to choose and/or modify a circuit in order to control the hot-carrier induced degradations. Finally we present an original application of our method: an ageing sensor dedicated for analog circuit based on hot-carrier induced degradation.

Integrated front-end for on line continuous calibration of Rogowski coil current transducer

The Rogowski coil is a traditional current-to-voltage transducer. To use it for high-accuracy measurement of low frequency AC current, it is necessary to have a very precise sensor geometry and very specific conditions, such as a stable temperature and a centered primary conductor in order to minimize errors. Conversely, it is also possible to compensate for these errors by using a sensor calibration. This paper presents a new continuous calibration system for Rogowski coil current transducer (RCCT). It features a reference conductor added close to the primary conductor and a calibration circuit which has been integrated in CMOS technology. First experimental results obtained with a homemade RCCT show that we drastically improve the immunity of the sensor to the primary conductor position with an error below ±2 % when the calibration is active against -8% to +4% without calibration. Limitations of the method are also discussed.

Towards multiphysics simulations of integrated circuits

Although the electrical benefits are greatly increasing in miniaturized integrated circuits, their corresponding design and reliability issues are also being raised. This work aims at the multiphysics simulation of integrated circuits that allows the designer to monitor the electrical, thermal and mechanical long term behaviour of the circuit from its early design stages. The multi-physics simulation tool is based on the direct method where three networks, i.e. an electrical, a thermal and a mechanical network, are directly linked and simulated with a unique circuit simulator. The tool was developed in a standard CAD environment, i.e. Cadence®. The way the three networks are built is described. In addition, to achieve multiphysics simulations, conventional CMOS models have to be replaced by specific multiphysics models that take additional physical effects into account, such as thermal effects, hot carriers induced ageing and their impact on the device performances. The modelling approaches as well as some simulation results are provided. Finally, the paper discusses the remaining prospective work to be able to perform electro-thermo-mechanical simulations of complex integrated systems.